The invention concerns an apparatus for measuring forces produced by unbalance of a rotary member as it rotates, for example a motor vehicle wheel.
A typical form of apparatus for measuring centrifugal forces produced in rotation of an unbalanced rotary member, for example as disclosed in German published specification (DE-AS) No 16 98 164, comprises a rotary member mounting arrangement for supporting the rotary member with respect to a frame structure. The rotary member and the rotary member mounting arrangement constitute a system which is oscillatable about an oscillation center, for applying centrifugal forces to a force-application location of at least one measurement pick-up which is supported on the frame structure. That apparatus therefore involves an oscillation-measuring, super-critical measurement system in which the rotary member is supported on leaf springs which are disposed inclinedly relative to each other and the prolongations of which form a virtual intersection in one of the balancing planes of the rotary member to be balanced. The two inclinedly disposed leaf springs are supported with respect to a base plate by way of an intermediate plate on leaf springs which are turned through 90xc2x0 relative to the first-mentioned inclined leaf springs and which are arranged in parallel relationship with each other and which are disposed perpendicularly. The assembly includes oscillation converters for detecting the oscillations of the leaf springs, which result from unbalance of the rotary member, and converting same into suitable measurement signals.
Attention may be directed in this respect to German published specifications (DE-AS) Nos 10 27 427 and 10 44 531 in which spring bars or leaf springs forming oscillatable mounting arrangements in balancing machines include reduced-thickness portions to form hinge or pivot means.
Reference may also be made to EP 0 343 265 A1 disclosing a balancing machine in which a support carrier which extends axially with respect to a measurement shaft on which a rotary member to be balanced is mounted in such a way as to be capable of oscillation with respect to a stationary frame structure, while measurement sensors which are disposed at an axial spacing from each other are arranged between the support carrier and the stationary frame structure.
DE 33 30 880 A1 discloses an arrangement in which a support assembly for carrying a rotary mounting structure for a measurement shaft is supported on a stationary frame structure by way of force measurement transducers arranged at an axial spacing from each other.
Reference may also be made to EP 0 133 229 A1 disclosing an apparatus which serves for balancing motor vehicle wheels, wherein a measurement shaft on which a motor vehicle wheel to be balanced is carried is supported on a frame in a mounting arrangement having force-measurement sensors. To provide for dynamic balancing, that machine has two mounting planes for supporting the measurement shaft, with the force-measurement sensors also being disposed in those mounting planes.
It will be noted in this respect that the measurement pick-ups or sensors which are disposed at the measurement locations in the mounting planes of the above-outlined apparatuses produce measurement signals proportional to the centrifugal forces which result from unbalance of the rotary member and which produce in the mounting planes or at the measurement locations, the reaction forces which are measured by the measurement sensors. Conventional standard measurement systems for wheel balancing machines usually employ a cantilever mounting configuration for supporting the measurement shaft and a rotary member to be balanced which is carried thereon. Conversion to the two balancing planes on the rotary member, to provide for dynamic balancing, is effected on the basis of the force-lever laws of statics. The forces measured by the force-measurement sensors in the above-mentioned mounting planes are therefore dependent on the respective spacing of the rotary member with respect to the two measurement sensors.
It will be appreciated that the differences in mass distribution which give rise to unbalance effects on the rotary member or rotational body involve resultants in respect of the centrifugal forces to be measured, which take effect at different axial positions and which are applied to the measurement sensors during a measurement run. The geometrical data of the measurement sensor linkage and the measurement planes give rise to transverse force components at the support locations of the measurement sensors, which cause phase shifts and have an adverse effect on the level of measurement accuracy.
An object of the present invention is to provide an apparatus for measuring centrifugal forces produced by an unbalanced rotary member, which can achieve a high level of measurement accuracy.
Another object of the present invention is to provide an apparatus for measuring centrifugal forces caused by unbalance of a rotary member as it rotates, which while being of a simple structure permits accurate measurement of the forces involved in a sub-critical mode of operation.
Still another object of the present invention is to provide an apparatus for measuring centrifugal force caused by unbalance of a rotary member as it rotates, wherein the rotary member is supported by a virtually rigid mounting configuration thereby to provide for an enhanced level of accuracy in terms of transmission of the centrifugal force to a measurement member.
In accordance with the principles of the present invention the foregoing and other objects are attained by an apparatus for measuring centrifugal forces produced by an unbalanced rotary member, comprising a support means such as a frame structure, and a rotary member mounting means for supporting the rotary member with respect to the support means. The rotary member and the rotary member mounting means form a system which is capable of oscillating about an oscillation center for applying centrifugal forces to a force-application location of at least one measurement sensor or pick-up which is supported on the support means. The rotary member mounting means and the rotary member which in operation of the apparatus is supported thereby and rotates in a measurement operation form a sub-critical oscillating assembly. The measurement sensor is a force pick-up means. The direction of application of force to the measurement sensor extends substantially tangentially with respect to a circular arc through the force-application location around the oscillation center.
As will be seen in greater detail from the description hereinafter of preferred embodiments of the invention, the invention provides that the support configuration for the rotary member mounting means and the measurement sensors which are used as force pick-up means is such that the result is a sub-critical oscillation system in which the spring forces involved are greater than the centrifugal forces of the unbalanced rotary member which rotates during a measurement run. The spring forces of the rotary member mounting means are so high that practically no spring deflection occurs and thus the rotary member mounting means form a rigid mounting. The apparatus has a cantilever mounting configuration, as is conventional in wheel balancing machines, for supporting the rotary member. In other words, the rotary member is secured to the measurement shaft at a location which is outside the location at which the measurement shaft is supported on the machine frame structure. The rotary member can be supported in the rotary member mounting means in such a way that support struts which are provided for that purpose intersect with their notional prolongations at an axis which forms the oscillation center of the sub-critical oscillation system. The direction of application of the centrifugal forces which are measured in a measurement run, to the measurement sensor which is in the form of a force pick-up means, extends substantially tangentially with respect to a circular arc through the force-application location around the oscillation center. The oscillation center can thus be defined by flexurally stiff supports, in particular two thereof, which can be of a generally plate-shaped configuration and which intersect at a linear intersection line forming a virtual mounting location for the rotary member in the rotary member mounting means. That virtual mounting location is tantamount to a virtual measurement location. That mounting location, of a linear configuration, extends substantially perpendicularly to the axis of the rotary member.
In a preferred feature of the invention the rotary member mounting means has a rotary mounting such as a mounting sleeve for supporting a measurement shaft on which the rotary member is fixed in a measurement run. As indicated above the rotary member may typically be a motor vehicle wheel.
The apparatus according to the invention can preferably be used for example in an arrangement as described in PCT/EP99/06372, corresponding to DE 198 39 976 A1. In that apparatus, the rotary mounting for the measurement shaft is supported on an intermediate frame structure by way of two flexurally stiff supports which can be of a plate-shaped configuration. The intermediate frame structure is in turn supported on a stationary frame structure by way of two further flexurally stiff supports which can also be plate-shaped. The supports of at least one of the two pairs thereof are arranged inclinedly relative to each other so that the prolongations thereof intersect at the oscillation center or the virtual mounting location substantially on the axis of the measurement shaft which also forms the axis of the rotary member. In addition the rotary mounting for the measurement shaft is supported on the intermediate frame structure by way of a first measurement sensor in the form of a force pickup means, and the intermediate frame structure is supported on the stationary frame structure by way of a second such measurement sensor in the form of a force pick-up means. In an embodiment of the present invention at least one of the two measurement sensors has a direction of application of force which is tangential with respect to the circular arc which passes through the respective force-application location and around the respective virtual mounting location.
In accordance with further preferred features of the invention the rotary mounting for the measurement shaft is supported with respect to the stationary frame at two support locations which are arranged at an axial spacing from each other and at which are arranged the measurement sensors which are here also in the form of force pick-up means. In this arrangement the assembly may form two virtual mounting locations or two real mounting locations.
It will be seen that, in the present invention, the centrifugal forces which occur during a measurement run by virtue of unbalance of the rotary member which is the subject of the measurement procedure are applied to the measurement sensor, with the same direction of application of force, by the rigid rotary member mounting means, irrespective of the respective mass distributions in the respective rotary members.
Further objects, features and advantages of the invention will be apparent from the description hereinafter of preferred embodiments of the invention.